Video data encoding circuit



June 9, 1964 J. l. DAsPlT 3,136,994

VIDEO DATA ENCODING CIRCUIT Filed June 19, 1956 '7 Sheets-Sheet 1 June 9, 1964 J. l. DAsPlT VIDEO DATA ENCODING CIRCUIT Filed June 19, 1956 '7 Sheets-Sheet 2 IN V EN TOR.

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June 9, 1964 J. l. DAsPlT VIDEO DATA ENCODING CIRCUIT '7 Sheets-Sheet 3 Filed June 19, 1956 ,fof/N femm-ws @psp/7' IN1/EN TOR.

June 9, 1964 J. l. DAsPlT VIDEO DATA ENCODING CIRCUIT 7 Sheets-Sheet 4 Filed June 19, 1956 June 9, 1964 J. l. DAsPlT VIDEO DATA ENcoDING CIRCUIT June 9, 1964 J. l. DAsPlT VIDEO DATA ENCODING CIRCUIT 7 Sheets-Sheet 6 Filed June 19, 1956 June 9, 1964 J. l. DASPIT VIDEO DATA ENcoDING CIRCUIT '7 Sheets-Sheet '7 Filed June 19, 1956 compressed.

United States atent 3,136,994 VIDE() DATA ENCGDING CRCUXT John I. 'Daspit, Santa Monica, Calif., assigner to Gilhllan Corporation, a corporation of California Filed June 19, 1956, Ser. No. 593,016 4 Claims. (Ci. 343-111) This invention relates to a video'data encoding circuit and method allowing bandwidth compression and, more particularly, to a circuit and method for encoding remote video data in a manner allowing transmission thereof over narrow bandwidth facilities such as telephone lines to a central station; the- .circuit and method having the further particular feature that no electronicV or mechanical synchronism is required between the means providing the remote video data and the encoding circuit.

The present invention forms an important subcombinational part of the system described and claimed in U.S. patent application Serial No. 593,011 for System and Method for Remote Radar Data Transmission and Coordinated Assembly at a Central Station by E.. I. Barlow et al. filed June l5, 1956, now US. Patent No. 2,972,141 issued February 14, 1961.` In this copending application a method is introduced for remote data transmission to a central station and transformation there into video data in the coordinates of the central station. An eiicient solution to the data assembly problem inherent in such a situation is provided. The encoder of the present invention nds particular application in the system of this copending application in providing means for compressing the video data so that it is suitable for transmission via narrow band facilities.

It will be understood, however, that the encoding circuit and method provided by the present invention are not necessarily limited to utilization in a system of the type described in the copending application. introduced herein may have a multitude of other applications which may arise in any situation `where data existing in a broadfrequency band must be compressed for a subsequent utilization.

In another attempt which has been made to solve the data compression problem, the Video data to be cornpressed in effectively regenerated and synchronously scanned at a lower rate. This technique allows compression by presenting the Video data a number of ltimes to ensure that a synchronized scanning signal coincides with atleast part of the video data which is regenerated.

In a particular mechanization the regenerating technique of the prior art is accomplished by visually displaying the video data on an intensity modulated circular l display, the cycle rate for the intensity l display The technique being synchronized in accordance with the scanning quired and the bandwidth of the transmission facilities available.

lNot only is it necessary to accurately synchronize the l dispiay control signals and the scanning control signals v but it is also necessary to generate the required azimuth 'synchronizing signals separately and to then mixthese synchronizing signals with the video data after it has been It should be apparent then that this technique necessitates a complexity of electronic circuits for synchronization, for separately generating synchronizing or reference signals, and for mixing these signals with the compressed video data signals.

The present invention obviates these and other disadvantages inherent in prior art approaches by providing a method and a circuit for compressing video data where a storage device is utilized to retain the video data information for a period corresponding to an antenna scanning cycle during which the stored data is read to provide compressed data suitable for transmission via narrow bandwidth facilities. The memory characteristic or decay time of the storage device is selected so that it is equal to or greater than a scanning cycle, thereby allowing the scanning to be performed at a rate which is independent of the rate of scanning utilized to provide the video data signals. This then obviates the `necessity of complicated synchronizing circuits which would otherwise be rcquired to ensure that the scanning rate for compression was accurately tied to the scanning rate for video data. signal generating.

Another feature provided by the storage and asynchronous scanning techniques of the present invention is that all reference and synchronizing signals which may be needed for subsequent decoding or display may be entered into appropriate positions in the memory device utilized. Thus the scanning device not only detects the compressed Video data but also automatically inserts the required synchronizing and reference signals. This has the further advantage in that variations in the scanning rate during a cycle will introduce a corresponding variation in the reference signal rate so that it is not necessary to regulate the scanning rate as accurately as is otherwiserequired.

In addition to providing a new approach to the video data compression problem which constitutes lan important step forward in the art, the invention also provides a specic circuit arrangement wherein the basic principles discussed above are embodied in a most economical and eicient manner. Thus in the particular mechanization which is described inV detail hereinafter, the video data to be compressed is first translated into a visual display which may be presented through the medium of a cathode ray tube. In the preferred practice of the invention this display is based upon rectangular coordinates allowing the simplest arrangement of display control circuits.

The visual display provided is then optically coupled to a scanning device, which preferably is a Vidicon camera tube. If the rectangular display is utilized, according to the preferred practice of the invention, thescanning device is also actuated in a simple manner with rectangular deflection coordinates to read out the visual information available on the display device. While the storage characteristic required may exist in the visual display device, in' the storage device, or in both, it has been found convenient in the practice of the invention to utilize the storage characteristic of a Vidicon tube rather than to rely upon specially` designed display devices such as the Graphicon more specifically referenced below.

in this particular mechanization of the invention, it has been found that theVidicon camera provides the required storage characteristic, if the accelerating potentials selected are lower than those utilized in'conventionalTV camera practice. The technique of lowering the potential lengthens the decay time of thelstorage characteristic and may allow storage time intervals exceeding 20 seconds.

Where the visual display storage technique is utilized, the desired reference and synchronizing signals which are to be transmitted along with the compressed video data are visually displayed in the proper reference position. Thus, in a particular application of the invention which is described, remote radar trigger and azimuth-gated rangemarking signals are displayed. In this manner the scanv` pending application.

. 3 ning device automatically generates azimuth-gated rangemarking signals and trigger signals at its own rate of scanning, thereby obviating the necessity of the separate generation and insertion of synchronizing signals.V These reference signals'then are readily decoded at a central station inthe manner described in the 'above-mentioned co- Accordingly, it is an objectV of the present invention to provide an encoding circuit for compressing the bandwidth of video data signals, without requiring complicated circuits'for synchronizing the encoding circuit with the video datasignal providing means.

Another object of the invention is to provide a method ing video datafor transmission through narrow band facilities Vwhere the video data is stored and scanned asynchronously, the storage step retaining the video data fora period equal to or greater than 'the' interval of a .scanning cycle.

vA more specic object is to provide a system for video i data transmission through narrow band facilities where the data is first translated to a visual display and then is scanned at a rate corresponding to the resolution desired and the frequency bandwidth available, either Vthe visual A display means or the scanning means providing a storage function corresponding to the scanning cycle.

Another specific object of the invention is to provide an encoding circuit for compressing the bandwidth of video data signals without requiring Vcomplicated circuits for synchronization, where the video data is iirst translated to a visual display on a cathode ray tube and is Ythen scanned asynchronously by meansof aVidicon camera and storage tube.

The novel features which are believedy to be'charac-V teristic of the invention, both as to its organization and method of operation, together with further objects 'and advantages thereof, will be better understood from Vthe following description considered in connection with the accompanying drawings. It is to be expresslyunderstood,

however, that the drawingsl are for the purpose of illusdefinitionof the limits of the invention.

FIG. .1 is a block diagram illustrating the general form ofa video'data encoding circuit according to the present invention; f Y

FIG. 2 is a schematic diagram of one form of azimuth sweep and gate signal generator which may be utilized in translation circuit 100 of the embodiment of FIG. 1;

tration and description only, and are not intended as a the circuits of FIG. 2 being arranged intoblock groupsV corresponding to the basic components utilized;

FIGS. 3a and 3b constitute afschematic diagram of a suitable form for display control 4circuits 300 forming part lof translation circuit 400 in theernbodiment of FIG. 1,

the circuits being also arranged in a block diagram form to indicate the basic components; Y

FIGS. 4a and 4b constitute. a schematic diagram illustrating ajsuitable form for the' circuits included in scanning means 400 of the embodiment ofKFIG..1, the block diagram arrangement beingagain utilized to indicate basic j components; and

1 FIG. 5 is a-'schematic of suitable form of theV output circuit 500 forming -part of theembodiment 01:V

FIG; 1, a block 'diagram' component arrangement also being emp1oyed. u

Reference is --noW made to` FIG. lgwhere the 'general form of encoding circuit allowing bandwidth compression,

according to the present invention, is shown in block diagram form. ."As indicated in FIG. l, video data and reference signals to be encoded are applied to translation means 100 which is-operative to prepare the applied 5 signals for storage, as will be more fully explained below.

In 'order to illustrate a particular form which translation means 100 may assume, twoA subcomponent circuits200 and 300 are shown which are particularly designed for the encoding of the remoteV radar and vtrigger signals and remote azimuth synchro data. Thus circuit 200 `is indicated to be an azimuthjsweep and gate signal generator Vand circuit 300 is'indicatedto vinclude display controlfcircuits which drive aV cathode ray tube device Y400CRT, forming part of circuit 400V described below.

Display device 400CRT is merely illustrative `of one 'means which may formnpa'rt of a storage and scanning circuit 400, the function of which yis'to translate input signals preparedV byV circuitV 100 into corresponding compressed video data vsignals which may be transmitted 20 through narrow band facilities.

In a particular form means 400 is indicated to include cathode ray tube device 400CRT and a TV camera and amplifier circuit 4.10, which may include a Vidicon tube, as is moreV specifically pointed outbelow. In order to illustrate'a specific utilization of the invention, as in Ythe o case of translating means 100, means 400 is indicated to include sweep control circuits-430 for actuating camera 410 to scan` the display provided by device 400CRT optically linked thereto through appropriate means not shown. Means 400 is also indicated as including a range sweep'generator 450 and an azimuth sweep generator 470 for controlling the corresponding operation of circuit V430 in la particular application where radar videodata is to be compressed for transmission.

Circuit 400 then provides compressed video output signals which are applied to an outputcircuit 500 suitable for driving narrow band transmission facilities' such as' a telephone line. As indicated circuit 500 may include Va narrow band video amplier stage 501 coupled to a single side band modulator and/orline driver circuit 502;.an-

- other arrangement being shown in FIG. 5.

'It-is important in mechanizing means 400 that a storage device be included allowing the -asynchronous operation of the scanning circuits with respect `to the-time of occurrence of thereference signals forming part of video data received by circuit 100. Thus theinvention may be practiced by utilizing a storagetube to provide-the visual display ofthe translated signals provided by circuit 100. For example, cathode ray-tube 400CRT. may be a ,Metrechon such as is described on pages 145-162 of anpa'rticleV entitledv The Metrechonf-a Half-Tone Picture. Storage Tube by L. Pensak published in the RCA Review, volume 15, 1954.. g Y f .Moreoven a double beamstorage tube may be utilized 5 where no visual display is.requ,ired,` the desired stored video-r data signal being ,availableY asl Vsemiconductive lcharges on a storagesurface. considered that cathode raytube 400CRT and TV camera `410 are integral parts of asingle unitsuch as a Graphicon,

a suitable form of which is'described. on pages A230--250 of an article entitled Graphicon` Writing Characteristics by A. H.Benneretral. published in RCA Review, volume l12,1une 1951. f, 1i However, it has been found convenient in the practice 6 of the invention to utilize a Vidiconcamera tube in com- V bination with a Vconventional cathode rayVV tube 'displayfdea Vice to provide the desired scanning and storage opera- 'Y tion. The characteristics of the` Vidicon tubeand associatedrcircuits will be considered in further detail below. However, it'will be understood .that fundamentallyother .storage media may be employed such asmagnetic tape or 1 drum 1 Y Another important thing to be noted in FIG.: 1 is. that Y according to the preferred practice of theinventionrany' 75 .reference signal which is vto be transmittedY .through the y In this situation itmay be'V tained.l i

aiaaasa v display provided and automatically generates appropriate reference or synchronizing signals which are properly positioned in time in relation to the video data displayed.

jIt will be understood, of course, that the visual display of reference marks is not required since these marks may as well be stored as a charge pattern or a series of magnetic spots.

The method of the invention will be better understood when specific circuit arrangements are considered, reference being made to FIGS. 2, 3a, 3b, 4a, 4b and 5. In these figures specific circuit mechanizations are indicated and suitable circuit parameters are designated, the con- Vention assumed throughout being that Vall resistors are specified in ohms, all capacitors in micromicrofarads, and all inductors in microhenrys unless otherwise specified.

While the specific arrangements shown in the figures are designed for a radar video data encoding application, it will be understood that many of the techniques employed may be utilized in general application. Thus the range and azimuth sweep circuits shown in FlG. 2 may be similar to vertical and horizontal deflection circuits where the video data forms part of a conventional TV raster.

Referring now to FlG. 2, it is noted that kremote azimuth synchro data signals are received by a resolver 210 having its rotor winding 211 coupled to an amplifier stage 220. The output signal produced by stage 22) is applied to a filter circuit 230 designed to provide a null response at the static frequency of resolver 2li) which may be 60 cycles in a particular application.

The signal produced by circuit 2.3i) then is effectively an error derivative signal which is amplified and split into two phases in a stage 224i) and applied to a push-pull amplier 250. Amplifier 25% is transformer coupled to one of the input windings of a motor control stage Zet). Control stage 260, it will be noted, includes a motor 251 which is rotated until the frequency dierence signal derived through stages 239, 24) and 250 becomes zero. The feedback loop required to achieve the required servo operation is effected by coupling motor Zul mechanically to the rotor 211 of resolver Zltl. Thus in this manner motor 261i is actuated to rotate in angular position under the control of remote azimuth synchro data signals applied to circuit Zitti.

This motor angular position then is converted to la `corresponding voltage through a signal generator circuit 255 which includes a potentiometer P265 having a rotatable center tap from which an azimuth sweep voltage corresponding to the remote azimuth angle may be ob- The azimuth sweep signal produced by circuit 265 is applied to a self-balancing deiiection amplifier 2?@ and to an azimuth blanking signal generator 289. While blanking circuit `23) may be of conventional design, circuit 27u is preferably of the self-balancing type. The specific circuitvarrangement indicated in circuit 2.79 is of this selfbalancing type.

Finally, circuit Zut) includes an azimuth gating signal t' generator 2% which provides an output signal utilized to control the gatingof range marking signals, as will be more fully understood when circuit Sii@ is considered with reference to PIG.3a. `As indicated a simple arrangeerence time which may conveniently be at zero azimuth.

This switch` operation thenis utilized in a well-known td manner to control the grid bias of a gating stage in circuit Bilt) to be described.

vReferring now to FIG. 3a, it is noted that, in a typical form where remote video radar signals are to be compressed, circuit 306 includes a video isolation amplifier' Siti which receives remote radar video and trigger signals and produces corresponding amplified output signals which are applied to circuit 315. The output signals produced by circuit 315 are combined in a nonadditive manner in a l.hier circuit 320 with range sweep unblanking pedestal signals produced by a range sweep gate circuit 33d, and with azimuth-gated range marking signals derived through gating circuit 335.

Range sweep gate 336 also controls a range marking oscillator 34u coupled through an amplifier 345 to a blocking oscillator stage 35d. The sharpened range marking signals produced by blocking oscillator 350 are then applied to gating circuit 335 which is operative to pass these signals to mixer circuit 320 upon each occurrence of an azimuth gating signal produced by circuit 290 introduced above. A signal is also obtained from blocking oscillator 35@ lmarking the end of the useful range scanning interval and is amplified through a stage 360 to produce a signal indicated to be a range-gate termination signal. This signal is applied to gate generator 330 to ensure the termination of the range gating signal produced thereby.

he range gating signals are also applied to a range sweep generator 370 which is coupled to a range deection amplifier 380 indicated again to be of the preferred Aself-*balancing type described in the corresponding abovementioned application by lohn Daspit.

The output signals provided by mixer stage 320 including amplified remote radar video, trigger signals, range unblanking signals, and azimuth-gated range marks, produced in the manner described above, are applied to a composite video amplifier stage 390 shown in FIG. 3b. The output signals produced by circuit 3% are then applied to display device dtlflCRT to control the corresponding display. In a similar mannerjhe azimuth flyback blanking signal produced by circuit 280 shown in FIG. 2, the range sweep signal produced by circuit 380 of FIG.

3a, and the azimuth sweep signal producd by circuit 274) of FIG. 2 are utilized to control display device MWCRT to provide the desired display. n

At this point it may be helpful to reconsider the function of the circuits just described with respect Ato the basic concept of the present invention. While many of the circuits described are conventional circuits which are utilized to provide a linear sweep display in rectangular coordinates, referred to in the art as a B display, several important modifications should be noted. It is important to note that trigger signals are amplified along with the remote radar video so that these marks form part of the display allowing an automatic generation of corresponding reference signals, as will be more fully understood when the scanning circuits of FIGS. 4a and 4b are described below.

Another' important modification is the utilization of an azimuth gating signal to control the passage of the range marking signals at 4a predetermined azimuth reference time. In this manner the desired range marks are available and an azimuth reference signal is conveniently presented sok that a separate ysignal generator and mixer circuit is obviated. y i y While the utilization of a linear or B display is not essential to the invention, such a display is preferred over other displays such as A,' 1, or,PPI displays, due to the simplicity in display and scanning circuits which are required, as well as the fact that the reference signals are readily encoded without the necessity of complicated circuits. Furthermore, the azimuth resolution at short ranges is better forthe B display than the PPI display. It will be understood, however, that the Y devices 471 Y and 473 v7 invention is not limited to the utilization of any particular type of visual display device since it willbe apparent that this is only one means of achieving the et al. in volume 23 of Electronicsn on page 70, May 1950.

It will be noted that circuit 410-1 includes suitable bias and potential supplying elements as are required for the proper operation of the Vidicon. WhileY these circuits are conventional, it is important to note that aV target voltage of approximately volts is utilized which is lower than conventional practice.

required in practicing the invention. It has been found with the speciiic circuit arrangement indicated in FIG. 4a that a storage time in excess of 10 seconds may be expected. Thus no difiiculty is obtained in utilizing an azimuth cycle rate Vof 10 seconds as will be explained Circuit 410 also includesa preamplifier 410-2, aV narrow band output amplifier 410-3, and a clamping circuit 410-4 for amplifying and eliminating noise from the compressed video signals. Y J

The scanning operation of Vidicon circuit 410-1 is controlled by range-and azimuth deflection amplifier circuits 431 and 432V forming the means of sweep control circuit 430 of FIG. l, which are coupled respectively to the range. and azimuth yokes 411R and 411A controlling the sweep of the Vidicon beam in tube 411-1. Deflection circuits 431 and 432 are actuated respectively by range and azimuth sweepgenerator circuits-451 and 471, shown in FIGS. 4a and 4b, respectively.

Range gating signals suitable for driving sweep generator 451 may be obtained by utilizing local 60-cycle power to drive a squaring amplifier 453, shown in FIG.

4b, providing a squarewave signal which may'then be frequency divided to the desired range sweep rate. In the arrangementtof FIG. 4b a frequency divider 455 is shown which essentially is a free-running .multivibrator which is synchronized by the signals received from circuit .453 at a submultiple frequencyspecifically selected thus f orm range sweep generator 450 of FIG. 1.

It .is important to note at this point thatthe range gating signals need not be synchronized in any VwayV with vthe actual remote trigger signals since the Vidicon scanning operation will automatically generate ysuch/'trigger signals as the Vidicon beam scans the corresponding Inasimilar. manner azimuth sweep generator 471 may lbe driven by a 60-cycle per s econdV synchronous motor '473 which is not in any waysynchronized with scan-Ef'S5 ningoperation of the remote video data providing means;

forming the azimuth sweep generator of FIG. l. V

- 4' It is important, 4however, 'that a fixed ratiobe maintained betweenvthe range sweep`rate and the azimuth sweep rate in order to allow proper decoding and d is-A Vplay 'where the encoded signals are utilized@ The reason forV this iswm/ore fully pointed out '5in the'ab'ovementioned copending-application by John vDvaspitvvhere the assembly system is`desc'ribed. Y t f Y Vidicon operating characteristics be Vselectedto ensr`e that the storage of the display charge pattern be main- This lowered potential allows a longer decay time for storage, as is Range gate generator 455 and azimuth sweep generator 471 are also coupled to a mixer and blanking signal generator stage 435, shown in FIG. 4b. This stage generates a flyback blanking signal which is mixed with Vthe output signals produced by preamplifier 410-2 shown in FIG. 4a and applied to circuit 410-3. Y The technique which is vutilized to form the blanking signal is conventional and therefore will not be describedin further` detail.

AsV in the case of the specific circuits illustratedas suitable for translation means 100, the specific'circuit arrangementV illustrated as suitable forcircuit- 400 may consist mainly of conventionalcircuits except for a few important modifications which must be introduced f or the purposes of the invention. Itf'is important 'thatthe tained for an interval which is equal to Vor greater than the azimuth scanning cycle rate illustrated specifically to be 10 seconds.

Furthermore, itis important to note the simplicity of cuits with trigger signals or azimuth synchro data. In

'to be 20 cycles per second. Circuits 451, 453 and'455 with the..signal (C-l-V)2 in an adder stage 545 toprothen applied to output circuit 500 shownrin specific illus- As indicated in FIG. 5 the compressed video data signals are applied to a clamptrative detail in FIG. 5.

ing circuit .510 which is designed to eliminate undesired noise. The'output signal provided by circuit 510 is applied to an amplifier stage 520 driving a low-passv filter 530 coupled Vto onek input'circuit of a doubly'balanced modulator circuit 540. It will be noted that the signal provided by filter 530 is designated as'a vsignal V indicating that it isV compressed video. Modulator 540 also receives a carrier'signal C provided by av carrier oscillator circuit 550. The carrier frequency is selected in accordance with the transmission facilities available, a

typical frequency being 1600 c.p.s.' for transmission through telephone facilities.

The output signal ofthe carrier oscillatoris designated as signal C, thesymbols tion according to the function (C-i-T/)2- (C-V 2.=4CV.

Thisoperation is achieved by phase splitting the carrier is squaredpto form the signalA (C-l- I/)in a balanced squaring Vstagef543. The signal (C-V)2 is inverted-inV a stage `5 44 to produce theY signal (C-I/)Z combined duce a signal4CV containing Vessentially only side bands. The' lower side band of signa1 4CV andra vestige of v'the upper wise band is then separated outthr'oughalow 'Abi v In a similar manvner the signal -i-Cf-is combined with Vthe signal V and.

VVC and V being utilized below to explain the operation f VVof modulator 540..

In brief, modulator 540 forms pure side band modulapass filter stage 560, the output signal ofwhich is mixed with the carriergsigiial Cinacarrier-side-bandy mixer. circuit -570.- The Voutputsignal produced by circuit 570''f` then contains the desired amount .of carrier and side band The signal produced bylcircuit 570 is VappliedfV to a line driver circuit 580 which is indicated to yinclude signals.

ia switchV 581`for selecting between the` carrier inode signal produced by circuit 570 and the raw video signal which is available direuyfrmamplinerszo. Irwin Ybe understood,ehowever, Vthat it is. not'essential thaththe.-

choice. between two modesof operation be available since sananet it is contemplated by the invention that either mode may be utilized. Furthermore, it Will be understood that the particular output circuit arrangement of FIG. is merely illustrative of a preferred circuit for driving a low band pass telephone line.

From the foregoing description it is apparent that the present invention provides a circuit and a method for encoding video data in a manner allowing transmission thereof over narrow bandwidth facilities where no electronic or mechanical synchronism is required between the means providing the remote video data and the encoding circuit.

What is claimed is:

l. In radar apparatus, the combination comprising: a cathode-ray tube having a luminescent screen; an antenna; rst means for pulsing said antenna to cause it to radiate a burst of energy; second means operable in synchronism with said rst means to gate the cathode-ray of said cathode-ray tube on in a manner to produce a plurality of marks on said screen spaced apart distances representing invariant intervals of time; third means to deect the cathode ray of said cathode-ray tube at a predetermined scan rate; and a camera positioned and connected to scan said cathode-ray tube at a rate slower than the scan rate of said cathode-ray tube.

2. In radar apparatus, the combination comprising a cathode-ray tube having a luminescent screen; an antenna; irst means for pulsing said antenna to cause it to radiate a burst of energy; second means operable in synchronism with said rst means to gate the cathode ray of said cathode-ray tube on in a manner to produce a plurality of marks on said screen spaced apart distances representing invariant intervals of time; third means to deect the cathode ray of said cathode-ray tube at a predetermined scan rate; and a camera including a Vidicon tube positioned and connected to scan said cathode tube at a rate slower than the scan rate of said cathode-ray tube.

3. In radar apparatus, the combination comprising: a cathode-ray tube having a luminescent screen; an antenna; rst rneans for rotating said antenna about a predetermined axis; second means responsive to rotation of said antenna and operable in synchronism with said rst means to gate the cathode ray of said tube on in a manner to produce a plurality of marks on said screen spaced apart distances representing invariant ranges of the angular position of said antenna; third means to deflect the cathode ray of said cathode-ray tube at a predetermined scan rate; and a camera positioned and connected to scan said cathode-ray tube at a rate slower than the scan rate of said cathode-ray tube.

4. In radar apparatus, the combination comprising: a cathode-ray tube having a luminescent screen; an antenna; first means for rotating said antenna about a predetermined axis; second means responsive to rotation of said antenna and operable in synchronism with said rst means to gate the cathode ray of said tube on in a manner to produce a plurality of marks on said screen spaced apart distances representing invariant ranges of the angular position of said antenna; third means to deflect the cathode ray of said cathode-ray tube at a predetermined scan rate; and a camera including a Vidicon tube positioned and connected to scan said cathode tube at a rate slower than the scan rate of said cathode-ray tube.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,219,021 Reisz Oct. 22, 1940 2,412,670 Epstein Dec. 17, 1946 2,415,981 \V0l` Feb. 18, 1947 2,422,295 Eaton June 17, 1947 2,430,283 Epstein Nov. 4, 1947 2,454,652 Iams et al. Nov. 23, 1948 2,524,295 Mesner Oct. 3, 1950 2,528,202 Wolff Oct. 31, 1950 2,595,691 Morton May 6, 1952 2,753,552 Ham July 3, 1956 2,861,263 McLucas Nov. 18, 1958 FOREIGN PATENTS 729,055 Great Britain May 5, 1955 

1. IN RADAR APPARATUS, THE COMBINATION COMPRISING: A CATHODE-RAY TUBE HAVING A LUMINESCENT SCREEN; AN ANTENNA; FIRST MEANS FOR PULSING SAID ANTENNA TO CAUSE IT TO RADIATE A BURST OF ENERGY; SECOND MEANS OPERABLE IN SYNCHRONISM WITH SAID FIRST MEANS TO GATE THE CATHODE-RAY OF SAID CATHODE-RAY TUBE ON IN A MANNER TO PRODUCE A PLURALITY OF MARKS ON SAID SCREEN SPACED APART DISTANCES REPRESENTING INVARIANT INTERVALS OF TIME; THIRD MEANS TO DEFLECT THE CATHODE RAY OF SAID CATHODE-RAY TUBE AT A PREDETERMINED SCAN RATE; AND A CAMERA POSITIONED AND CONNECTED TO SCAN SAID CATHODE-RAY TUBE AT A RATE SLOWER THAN THE SCAN RATE OF SAID CATHODE-RAY TUBE. 